[avar]

For some historical context: The debate over whether using the publicly advertised functions of a GPL library makes your code GPL too is an old one, the best and early example of this was the CLISP v.s. FSF debate, which the FSF won: http://clisp.cvs.sourceforge.net/viewvc/clisp/clisp/doc/Why-... in particular Stallman said:

    I say this [that using the readline API makes your code GPL too]
    based on discussions I had with our lawyer long ago.  The issue
    first arose when NeXT proposed to distribute a modified GCC in two
    parts and let the user link them.  Jobs asked me whether this was
    lawful.  It seemed to me at the time that it was, following
    reasoning like what you are using; but since the result was very
    undesirable for free software, I said I would have to ask the
    lawyer.
    
    What the lawyer said surprised me; he said that judges would
    consider such schemes to be "subterfuges" and would be very harsh
    toward them.  He said a judge would ask whether it is "really" one
    program, rather than how it is labeled.

Later, Linux under the direction of Linus Torvalds did the opposite the other way by looking the other way when nVIDIA and others distributed binary blobs that directly interfaced with the kernel. Some people now point to this as an example of why this sort of thing is just fine by the GPL, but in fact it's a very grey area. It's likely that if the Linux kernel had been run by the FSF that nVIDIA's actions would have resulted in a lawsuit.

However, as pointed out by others this doesn't appear to be a case of using a public GPL API at all, but rather case of code being copied. See http://drewblas.com/2010/07/15/an-analysis-of-gpled-code-in-... specifically this comparison: http://drewblas.files.wordpress.com/2010/07/diff.png